// Copyright 2017 The Abseil Authors.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//      https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

// The implementation of CycleClock::Frequency.

//

// NOTE: only i386 and x86_64 have been well tested.

// PPC, sparc, alpha, and ia64 are based on

//    http://peter.kuscsik.com/wordpress/?p=14

// with modifications by m3b.  See also

//    https://setisvn.ssl.berkeley.edu/svn/lib/fftw-3.0.1/kernel/cycle.h

#include "absl/base/internal/cycleclock.h"

#include <atomic>

#include <chrono>  // NOLINT(build/c++11)

#include "absl/base/attributes.h"

#include "absl/base/config.h"

#include "absl/base/internal/unscaledcycleclock.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace base_internal {

#if ABSL_USE_UNSCALED_CYCLECLOCK

ABSL_CONST_INIT std::atomic<CycleClockSourceFunc>

    CycleClock::cycle_clock_source_{nullptr};

void CycleClockSource::Register(CycleClockSourceFunc source) {

  // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.

  CycleClock::cycle_clock_source_.store(source, std::memory_order_release);

}

#ifdef _WIN32

int64_t CycleClock::Now() {

  auto fn = LoadCycleClockSource();

  if (fn == nullptr) {

    return base_internal::UnscaledCycleClock::Now() >> kShift;

  }

  return fn() >> kShift;

}

#endif

#else

int64_t CycleClock::Now() {

  return std::chrono::duration_cast<std::chrono::nanoseconds>(

             std::chrono::steady_clock::now().time_since_epoch())

      .count();

}

double CycleClock::Frequency() {

  return 1e9;

}

#endif

}  // namespace base_internal

ABSL_NAMESPACE_END

}  // namespace absl